282 SANTE NACCARATI 



In the Anura, also, the thyreoid is a double organ (single in 

 the emb'ryo), lateral, egg-shaped, pmkish in color; each half is 

 4 mm. in diameter; both are located m the ventral side of the 

 animal, at the posterior horns of the hyoid bone, in front of the 

 jugular veins, to which they are closely adherent. 



In the Ophidia the thyreoid is a single discoidal organ located in 

 the median line at the base of the heart, between the two carotids 

 in the young animal it is at the lower extremity of the thymus. 

 Its diameter is about 3 nam. and its weight about 2 mgm.; by 

 its grayish-white color it is easily distinguished from the two 

 thymous lobes, noticeable for their brighter color, whose medial 

 margins cover it. 



In the Lacertilia also (aside from a few genera like Monitor, 

 in which it consists of two lobes located at the side of the neck 

 in front of the carotids) the th>Teoid is a single medial organ 

 just under the skin on the ventral side of the trachea, along which 

 it Hes with its greatest diameter transverse to the diameter of the 

 trachea. It is dark gray; fusiform, largest in the middle, the 

 two extremities narrowing until, as they reach the lateral ex- 

 tremities of the neck, they terminate in a fine filament, often 

 bifurcated. In the Laeerta viridis it reaches a length of 1 cm. 



My research on the thyreoid in the Squamata, on the species 

 Zamenis viridifla\ais, Tropidonotus natrix, Laeerta viridis, and 

 Laeerta agihs, confirming this statement, will form the subject 

 of another paper. 



In the Aves the thyreoid consists of two rounded or oval lobes, 

 pink in color, varying in size with the animal, and located at the 

 sides of trachea near the syrinx, attached to the ventral side 

 of the carotid, generally at the level of the vertebral artery. In 

 the pigeon, for example, the thyreoids occur in the anterior wall 

 of the thorax, near the junction of the thorax and neck. They 

 are o\ailar in form, ^dth their longest diameter lengthwise of the 

 body; their lowest point is slightly above the pomt where the 

 main branches of the carotid artery divide. In front of them are 

 the jugular veins on the outside and the oesophageal arteries on 

 the inside. 



